The ability to predict how corrosive a crude oil or its distilled fractions will be during high temperature processing in contact with steel and other materials of containment would be highly useful to those involved in the extracting, processing and refining of petroleum. With such corrosivity information, refiners would have a more accurate understanding of the risks involved in processing a proposed crude or its distillates. For example, if a crude oil contains a high level of corrosive species, special care could be taken in processing it, while a crude oil containing fewer corrosive species could be processed confidently with standard safeguards in place. Other strategies could be employed such as blending the oil with different crudes to reduce the concentration of corrosive species. Thus, having the ability to predict corrosivity would reduce risk levels and enable smarter strategies in processing a variety of crude oils.
One element found in crude oils and known to cause corrosion is sulfur. An industry standard for predicting the rates of sulfidation, known as the “modified McConomy curves,” shows corrosion rate of various alloys as a function of temperature using empirical data of crudes with 0.6 wt. % sulfur. To account for varying concentrations, a correction factor for increasing sulfur content is included. While the total amount of sulfur in crude can be measured quite easily, this value is not a very accurate indicator of how corrosive a crude oil will be when it is processed at elevated temperature. This lack of correlation stems from the large range of reactivity that exists between various types of organic sulfur compounds found in petroleum and metals. These differences are apparent in high temperature tests of steel coupons exposed to gaseous streams of individual sulfur compounds containing the functional groups found in crude, with disulfides showing at least an order of magnitude greater sulfidation rate than thiophenes. Ranking of corrosivity by sulfur compound types has been done for idealized lab samples, but not for real crude oil samples because of the inability to measure how much of sulfur compound type is in the oil.
There exists a need for a method which would identify corrosive species and relative amounts of the corrosive species in crude oil and its distilled fractions to aid in predicting how corrosive a specific type of crude oil or distilled fraction is likely to be.